The present invention is related to an improved alkylation/transalkylation process which utilizes a dual reactor system employing dissimilar catalysts to produce a monoalkylaromatic product. More specifically, this invention involves the use of a noncrystalline (also known as amorphous) silica-alumina material to catalyze the alkylation reaction, and an inorganic oxide bound crystalline aluminosilica material acid treated after formulation into a catalyst particle to catalyze the transalkylation reaction. The invention also relies upon a synergism of the two reaction zones and a separations zone to produce a high purity monoalkylated aromatic product while producing negligible amounts of undesirable product poisons and heavy by-products.
The alkylation of aromatics with an alkylating agent in the presence of an alkylating reactant is a process well known for its ability to produce such monoalkylaromatic products as ethylbenzene, cumene, linear alkylbenzenes and so forth. Such monoalkylaromatic compounds are important chemical precursors in the production of detergents and polymers among others. Alkylation catalysts that are known to produce alkylaromatic compounds include the well known Friedel-Crafts catalysts; sulfuric acid, phosphoric acid, hydrofluoric acid, and aluminum chloride in either liquid or solid supported form. Solid granular catalysts such as clays, zeolites, and amorphous materials have also been utilized as alkylating reactants in both a modified and naturally occurring form.
The use of a transalkylation reaction zone in conjunction with an alkylation reaction zone for the production of monoalkylaromatics is also well known. A transalkylation reaction zone employed in a process in conjunction with an alkylation reaction zone enables the alkylation reaction zone to be operated at higher conversion conditions due to the ability of the transalkylation reactant to convert the undesired polyalkylaromatic compounds produced by the higher alkylation zone conversion conditions into desired monoalkylaromatic compounds. Translakylation catalysts that are known to have utility in the production of alkylaromatics from polyalkylaromatics include Friedel-Crafts catalysts such as sulfuric acid, phosphoric acid, aluminum chloride in either the liquid or solid supported form, and the like. Solid granular catalysts such as clays, zeolites, and amorphous materials have also been utilized as transalkylation reactants.
A myriad of processing schemes employing an alkylation reaction zone, a transalkylation reaction zone, and a separations zone, and employing various product, feed, and intermediate product recycles are well known to produce monoalkylaromatic products in high yields. One drawback concerning existing alkylation/transalkylation processes is the potential for the alkylation and/or the transalkylation catalyst to produce undesirable products such as alkylting agent oligomers, heavy polyaromatic compounds, and unwanted monoalkylaromatics. The alkylating agent oligomers can be especially troublesome as they re often recovered with the desired monoalkylaromatic product where they can detrimentally affect the utility of the monoalkylaromatic product in further conversion processes. An example of this would be the contamination of cumene with propylene oligomers which may reduce the utility of using such contaminated cumene as a phenol process feedstock and ultimately for the production of phenolic resins due to the presence of the oligomers as an inert compound within the cross-linked resins.
Another drawback inherent to some existing alkylation/transalkylation processes is the use of Friedel-Crafts catalysts such as solid phosphoric acid or hydrofluoric acid as the alkylation and/or transalkylation catalysts. Many of these catalysts require a water cofeed and produce an extremely corrosive sludge by-product. The utilization of such sludge-producing catalysts in an alkylation process requires that special design considerations be made regarding unit metallurgy, safety, and by-product neutralization. Such design considerations are typically costly and may add significantly to the construction and operations costs of such processes. Additionally, the use of Friedel-Crafts catalysts requires a once-through processing scheme to ensure that damaging corrosive materials are not recycled into the reaction zone. This requirement necessitates the operation of the process at high conversion conditions which tend to produce greater amounts of unwanted by-products such as alkylating agent oligomers and heavy by-products.